Your teacher probably wants you to think on a different way. Instead of implementing the blocks each in a single transfer function block, you can use your knowledge that two transfer functions behind each other in a block diagram mean mathematically multiplying them:
If the first block from the block diagram is sys1 and the second is sys2, you can exchange the two with just one whole sys transfer function. If you don't want to calculate it on paper, use matlab to calculate what transfer function results:
sys2=tf(,[5 1 0])
The result will be displayed in the form you are used to it. It you don't know how the numbers in the brackets are entered, read:
It explains how the numerator and denumerator from a transfer function are entered to the function and also, the exact same numerator / denumerator form applies for simulink!
Finally, delete the gain in simulink and change the numerator and denumerator block to the values you just got by multiplying the two functions.
Or: Probably you figured out that if you leave the gain 5 outside, multiplying the two system is like placing the first function 1+ 0.8s on top of the second function, because the second function only has a numerator of 1.
P.s.: In your Simulink transfer function block, you have too many '5's